This invention relates to x-ray analysis systems and methods.
X-rays or gamma-rays can be used to measure the density and distribution of bone in the human body in order to help health professionals assess and evaluate projected bone mineral density, which in turn can be used to monitor age-related bone loss that can be associated with diseases such as osteoporosis. Additionally or alternatively, similar procedures can be used to measure non-bone related body content such as body fat and muscle.
In general, in bone densitometry a patient is placed on a table while a radiation source irradiates the patient. An x-ray detector is positioned on the opposite side of the patient from the source to detect the radiation transmitted through the patient. The x-ray source and detector are usually mechanically linked by a structure such as a C-arm to ensure alignment of source and detector. Both x-ray tubes and isotopes have been used as a source of the radiation. In each case, the radiation from the source is collimated to a specific beam shape prior to reaching the patient to thereby restrict the field of x-ray or gamma radiation to the predetermined region of the patient opposite which are located the detectors. In the case of using x-rays, various beam shapes have been used in practice including fan beam, pencil beam and cone or pyramid beam shapes.
The shape of the beam and the shape of the detector system correspond. The detector in a fan beam system typically is a linear array of detectors. Some examples of the actual detectors which make up the array are the relatively low cost silicon photo diodes coupled with a scintillation material and the relatively high cost photo multiplier tubes coupled with scintillation material. In both cases, the cost of the detector system and associated electronics increases substantially with increasing numbers of detectors.
By means of mechanically moving the source/detector system relative to the patient, the fan beam of x-rays can be scanned in a direction normal to the plane defined by the boundaries of the fan beam angle to produce a rectangular analysis area. The width of this rectangular area is defined by the width of the fan beam when it passes through the patient. Of course, it is desirable that the scanned area include the desired region of analysis.
Typical regions of analysis in bone densitometry include the spine, hip and wrist, scanned individually. They can be covered individually within a reasonable time by a fan beam that has a relatively narrow angle in a single pass or, alternatively, by a pencil beam scanning a raster pattern. Another analysis region is termed "oblique hip" in which the hip is viewed at an angle relative to the horizontal and vertical directions. This can be desirable for optimizing the projection angle through the femoral neck. However, current techniques typically require patient leg positioning which can result in imprecise measurements on repeated scans of the same patent.
Another analysis region is referred to as "whole body" in which the entire patient body is scanned and analyzed for bone density and possibly also for "body composition" or the percentages of fat and muscle in the body. Known whole body procedures have utilized pencil beam scans of the patient, using a relatively narrow beam of radiation and a single detector scanning the whole body in a raster scan. However, such a scan takes a considerable length of time. If the whole body is to be scanned in a single pass with a fan beam of radiation, the fan angle would have to be considerably greater than that required for other typical analysis such as hip, spine or wrist analysis. This implies that the detector array must also be substantially wider than an array for wrist, hip or spine analysis if whole body analysis is to proceed by using only pass of the beam over the patient. Alternatively, one could utilize multiple longitudinal passes of the patient body using a smaller and less expensive detector array but the data from the multiple passes would need to be merged without artifacts especially at the boundaries between passes.
Known system of this type are manufactured by the assignee hereof under the tradenames QDR-2000, QDR-1500, QDR-1000plus, and QDR-1000. The following commonly owned U.S. Pat. Nos. pertain to such systems and are hereby incorporated by reference herein: 4,811,373, 4,947,414, 4,953,189, 5,040,199, 5,044,002; 5,054,048, 5,067,144, 5,070,519, 5,132,995 and 5,148,455; and 4,986,273 and 5,165,410 (each assigned on its face to Medical & Scientific Enterprises, Inc. but now commonly owned). Other bone densitometry systems are believed to be offered by the Lunar Corporation of Madison, Wis. (see, e.g., the system which is believed to be offered under the tradename Expert and U.S. Pat. No. 5,228,068, neither of which is admitted to be prior art against this invention).